A conventional method for resolving non-uniform brightness of the LEDs in a LED display device is selecting LEDs having similar brightness, or utilizing correction bits to correct the brightness of each dot. The latter method is possible by increasing the control bits of the pulse width modulation (PWM) signal.
As shown in FIG. 1A, considering the situation of dividing the brightness into 256 gray levels as an example, the brightness of the driven LED can be adjusted by pulse width modulation technology. The pulse width shown in FIG. 1B represents 1/256 of full brightness. The pulse width shown in FIG. 1C represents 3/256 of full brightness. For example, the brightness of the LED display device is originally designed to have 64 gray levels, wherein 6-bits are used. But due to the non-uniform brightness of the LEDs, additional 2-bits may be used for the purpose of brightness correction.